1. Field of the Invention
The present invention relates to a laser irradiating apparatus and method.
2. Description of Related Art
Conventionally, laser light is used to crystallize or anneal a semiconductor layer in manufacture of a semiconductor device.
In processing a subject surface by laser light irradiation or in performing annealing or crystallization by laser light irradiation to form a semiconductor film, a high-vacuum state is once established in a chamber where laser light irradiation is to be performed (called a laser irradiation chamber in this specification) by a vacuum pump before the laser light irradiation is started. Thus, a gas such as oxygen is introduced into the chamber to provide a pressure suitable for processing.
However, there is a problem that when crystallization to form a semiconductor film is performed by laser light irradiation according to the above procedure, a resulting semiconductor film does not have proper characteristics.
Further, where a semiconductor layer is irradiated with laser light in the laser irradiation chamber, there occurs a phenomenon that Si that constitutes the semiconductor layer or a metal such as B or P (in irradiation after ion implantation) is emitted from an irradiated portion of the semiconductor surface and sticks to the inside surfaces of the irradiation chamber.
If such impurities stick to, for instance, a window through which laser light is to pass, there occur various problems such as reduction in laser light intensity. Conventionally, when the inside of the laser irradiation chamber is polluted in this manner, the inside of the chamber is cleaned to eliminate pollutants, which is conducted every time laser processing is performed a predetermined number of times. For example, this is done such that the irradiation chamber itself is disassembled and pollutants are wiped off the components being immersed in a cleaning liquid.
It may also be the case that a native oxide film, an organic material, or the like is formed on a substrate.
However, where pollutants (contaminations) are removed by cleaning the inside of the laser irradiation chamber, the cleaning takes long time, resulting in a considerable reduction in the operation efficiency of the laser irradiation apparatus. It is desired to solve this problem.
Where a semiconductor layer is crystallized or annealed in such a polluted laser irradiation chamber in a process of manufacturing thin film transistors (TFT), pollutants influence the characteristics of completed TFTs.